Centralized control architecture for a plasma arc system

ABSTRACT

The invention features a centralized control architecture for a closely-coupled plasma arc system, in which the “intelligence” of the system is integrated into a single controller. The closely-coupled plasma arc system includes a power source, an automatic process controller and a torch-height controller, where each of these components individually has a closed-loop dynamic relationship with the controller.

FIELD OF THE INVENTION

The present invention relates to a centralized control architecture foroperating a plasma arc system.

BACKGROUND OF THE INVENTION

Plasma arc systems are widely used for cutting metallic materials andcan be automated for automatically cutting a metallic workpiece. Ingeneral, a plasma arc system includes a plasma arc torch, an associatedpower supply, a remote high-frequency (RHF) console, a gas supply, apositioning apparatus, a cutting table, a torch height control, and anassociated computerized numeric controller. FIG. 1 shows an example of aplasma arc system.

In operation, a user places a workpiece on the cutting table and mountsthe plasma arc torch on the positioning apparatus to provide relativemotion between the tip of the torch and the workpiece to direct theplasma arc along a processing path. The user provides a start command tothe computerized numeric controller (CNC) to initiate the cuttingprocess. The CNC accurately directs motion of the torch and/or thecutting table to enable the workpiece to be cut to a desired pattern.The CNC is in communication with the positioning apparatus. Thepositioning apparatus uses signals from the CNC to direct the torchalong a desired cutting path. Position information is returned from thepositioning apparatus to the CNC to allow the CNC to operateinteractively with the positioning apparatus to obtain an accurate cutpath.

The power supply provides the electrical current necessary to generatethe plasma arc. The power supply has one or more dc power modules toproduce a constant current for the torch. Typically, the current can beset to discreet values. The power supply has a microprocessor, whichregulates essentially all plasma system functions, including startsequence, CNC interface functions, gas and cut parameters, and shut offsequences. For example, the microprocessor can ramp-up or ramp-down theelectrical current. The main on and off switch of the power supply canbe controlled locally or remotely by the CNC. The power supply alsohouses a cooling system for cooling the torch.

The gas console controls flow of plasma and shield gases to the torch.The gas console houses solenoid valves, flow meters, pressure gauges,and switches used for plasma and shield gas flow control. The flowmeters are used to set the preflow rates and cut flow rates for theplasma and shield gases. The gas console also has a multi-inlet gassupply area where the required plasma and shield gases can be connected.A toggle switch can be used to select the plasma gases. The plasma andshield gases are monitored by gas pressure gages. In order to operatethe gas console, all settings must be manually selected.

The RHF console houses a high frequency starting circuit that is used tofire the torch. The RHF console also houses a cathode manifold used tointerface power and coolant leads between the power supply and thetorch. The power and coolant leads and a pilot arc lead make up ashielded torch lead set which connects with the torch. In addition, gaslines are also supplied to the torch to supply gas.

The torch height control sets the height of the torch relative to thework piece. The torch height control, typically, has its own controlmodule to control an arc voltage during cutting by adjusting thestandoff, (i.e., the distance between the torch and the work piece), tomaintain a predetermined arc voltage value. The torch height control hasits own external control module to control the standoff. The torchheight control has a lifter, which is controlled by the control modulethrough a motor, to slide the torch in a vertical direction relative tothe work piece to maintain the desired voltage during cutting.

The plasma arc torch generally includes a torch body, an electrodemounted within the body, passages for cooling fluid and cut and shieldgases, a swirl ring to control the fluid flow patterns, a nozzle with-acentral exit-orifice, and electrical connections. A shield can also beprovided around the nozzle to protect the nozzle and to provide a shieldgas flow to the area proximate the plasma arc. Gases applied to thetorch can be non-reactive (e.g. argon or nitrogen) or reactive (e.g.oxygen or air).

In operation, the tip of the torch is positioned proximate the workpieceby the positioning apparatus. A pilot arc is first generated between theelectrode (cathode) and the nozzle (anode) by using, for example, a highfrequency, high voltage signal from the RHF console. The pilot arcionizes gas from the gas console passing through the nozzle exitorifice. As the ionized gas reduces the electrical resistance betweenthe electrode and the workpiece, the arc transfers from the nozzle tothe workpiece. The torch is operated in this transferred plasma arcmode, which is characterized by the conductive flow of ionized gas fromthe electrode to the workpiece, to cut the workpiece.

The plasma arc system as described above has high cycle time. First, atorch operator must know some basic cutting parameters, such as thematerial to be cut, the thickness of the workpiece, and the plasma gasto be used. Then, the operator must review a series of tables found inbooks to manually set many parameters such as the power settings on thepower supply or the gas flow on the gas console. Having to look tipadditional parameters takes time and may result in operator error asmanual input can be inaccurate.

In addition, some components such as the torch height control and thepower supply have their own control, which can be redundant.Furthermore, there is no feedback mechanism between the components ofthe plasma arc system to optimize the operation of the plasma arcsystem.

SUMMARY OF THE INVENTION

The present invention relates to a control architecture for a plasma arccutting system. In particular, the invention relates to a centralizedcontrol architecture for a plasma arc cutting system, in which the“intelligence” of the system is integrated into a single controller.

In one aspect, the invention features a method of controlling anintegrated plasma arc system. According to one embodiment of the method,a first group of process parameters are input into a controller. Asecond group of process parameters are generated based on the firstgroup of process parameters. At least one command signal is providedfrom the controller to at least one auxiliary device to control anoutput parameter generated by the at least one auxiliary device. Atleast one auxiliary device is either a power supply or an automaticprocess controller. The output parameter generated by the auxiliarydevice is detected and the command signal provided to the auxiliarydevice is adjusted based on the detected output parameter.

At least one auxiliary device can be the automatic process controller.The pressure of gas exiting the automatic process controller can bedetected and the command signal provided to the automatic processcontroller for controlling the gas flow can be adjusted based on thepressure. At least one auxiliary device can be the power supply. Afeedback signal generated by the power supply indicative of an arcvoltage at the plasma arc torch can be detected and the command signalprovided to the power source for controlling a current output can beadjusted based on the feedback signal.

At least one auxiliary device can include a first auxiliary device and asecond auxiliary device. A first output parameter generated by the firstauxiliary device can be detected and the command signal provided to thesecond auxiliary device can be adjusted based on the first outputparameter. For example, the first auxiliary device can be the automatedprocess controller and the second auxiliary device can be the powersupply. The pressure of an outlet gas exiting the automated processcontroller can be detected and the command signal provided to the powersupply for controlling an output current can be adjusted based on thepressure. A feedback signal generated by the power supply indicative ofan arc voltage of the plasma arc torch can be detected and the commandsignal provided to the automatic process controller for controlling thegas flow can be adjusted based on the feedback signal. Alternatively,the first auxiliary device can be the power supply and the secondauxiliary device can be a torch height controller. The feedback signalgenerated by the power supply can be detected and the command signalprovided to the torch height controller for controlling a standoff canbe adjusted based on the feedback signal.

The method of controlling the integrated plasma arc system can alsoinclude the step of monitoring a life of a consumable of the plasma arctorch. The life of the consumable can be monitored and the commandsignal provided to at least one auxiliary device can be adjusted basedon the monitored life of the consumable. The pressure of gas exiting theautomatic process controller and/or the arc voltage at the torch can becompared to a reference value to determine the wear of the consumable.The flow rate of gas provided to the plasma arc torch and/or the cuttingcurrent can be adjusted to compensate for the wear of the consumable.

In another aspect, the invention features a method of controlling anoperation of a plasma arc torch system, which includes an automaticprocess controller in electrical communication with a computerizednumeric controller and in fluid communication with a plasma arc torch.The automatic process controller has at least one valve and at least onesensor. According to the method, a command signal is provided from thecomputerized numerical controller to the valve to control a flow of atleast one gas to the plasma arc torch. A condition of the gas exitingthe automatic process controller is monitored using the sensor. Thecommand signal provided to the valve is adjusted based on the monitoredcondition.

In one embodiment, a first command signal is provided to a first valveto control the flow of a cut gas and a second command signal is providedto a second valve to control the flow of a shield gas. The pressure ofthe cut gas is monitored using a first pressure transducer and thepressure of the shield gas is monitored using the second pressuretransducer. The first command signal provided to the first valve isadjusted based on the pressure of the cut gas monitored by the firstpressure transducer. The second command signal provided to the secondvalve is adjusted based on the pressure of the shield gas monitored bythe second pressure transducer.

In one aspect, the invention features a controller for an integratedplasma arc system. The controller includes an input module, a referencemodule, at least one interface module, and a detection module. The inputmodule receives a first group of process parameters from a user foroperating the plasma arc system. The reference module generates a secondgroup of process parameters for operating the plasma arc system based onthe first group of process parameters. At least one interface moduleinterfaces with at least one auxiliary device of the plasma arc systemand provides at least one command signal to the auxiliary device tocontrol an output parameter generated by the auxiliary device. At leastone of the auxiliary device is a power supply or an automatic processcontroller. The detection module monitors the output parameter generatedby the auxiliary device and adjusts the command signal provided to theauxiliary device.

The auxiliary device can be a power supply and the detection module canmonitor a current output generated by the power supply. The auxiliarydevice can be an automatic process controller for controlling gas flowto the plasma arc torch and the detection module can monitor pressure ofthe gas and adjust the command signal provided to a valve in theautomatic process controller based on the pressure. The gas can be a cutgas and/or a shield gas.

In another aspect, the invention features a control system forcontrolling an operation of a plasma arc system. The control systemincludes an automatic process controller and a computerized numericalcontroller (CNC) in electrical communication with the automatic processcontroller. The automatic process controller includes at least one valvefor controlling a flow of at least one gas to a plasma arc torch and atleast one sensor for monitoring a condition of the gas. The CNCgenerates at least one command signal for operating at least one valve,receives the condition monitored by at least one sensor, and adjusts thecommand signal based on the condition monitored by the sensor.

The automatic process controller can include a first manifold forcontrolling flow of a cut gas and a second manifold for controlling flowof a shield gas. Two cut gases can be mixed in the first manifold. Theautomatic process controller can include a first proportional flowcontrol valve positioned upstream of the first manifold for controllinga cut gas flow to the first manifold and a first pressure transducerpositioned downstream from the first manifold to measure pressure of thecut gas exiting the first manifold. The automatic process controller caninclude a second proportional flow control valve positioned upstream ofthe second manifold to control a shield gas flow to the second manifoldand a second pressure transducer positioned downstream from the secondmanifold to measure pressure of the shield gas exiting the secondmanifold. The first proportional flow control valve can be adjustedbased on the pressure of the cut gas measured by the first pressuretransducer. The second proportional flow control valve can be adjustedbased on the pressure of the shield gas measured by the second pressuretransducer.

In another aspect, the invention features an integrated plasma arcsystem. The system includes a controller, a power source, a plasma arctorch, an automatic process controller, and a torch height controller.The power source is in electrical communication with the controller. Thepower source generates an electrical current sufficient to form a plasmaarc. The plasma arc torch is in electrical communication with the powersource through a torch lead. The automatic process controller is inelectrical communication with the controller. The automatic processcontroller is positioned to control delivery of gas from the powersource to the plasma arc torch. The torch height controller is inelectrical communication with the controller. The torch heightcontroller is positioned to control a standoff between the plasma arctorch and a workpiece. The controller is physically remote from thepower supply, the torch height controller and the automatic processcontroller. The controller controls, monitors and adjusts an outputparameter of each of the power supply, the automatic process controllerand the torch height controller for operation of the plasma arc system.

In one embodiment, the system also includes a table and a drive systemfor moving the plasma arc torch over a cutting surface of the table. Thecontroller provides a command signal to the drive system to position thedrive system and receives a feedback signal from the drive system tomonitor a position of the drive system.

In another aspect, the invention features a plasma arc system whichincludes a power source and a controller in electrical communicationwith and physically remote from the power source. The power sourcegenerates an electrical current sufficient to form a plasma arc in aplasma arc torch. The controller controls, monitors, and adjusts theelectrical signal generated by the power source.

The power source can include an input, a switch, a main transformer, atleast one dc power module, and torch ignition circuitry. The inputreceives an input signal. The switch can be in electrical communicationwith the input and the controller. The switch can receive a switchcommand signal from the controller to open or close the switch. The maintransformer can be in electrical communication with the switch toreceive the input signal when the switch is closed and generates an ACoutput signal. The dc power module can be in electrical communicationwith the main transformer and the controller. The dc power module canreceive the AC output signal from the main transformer and a dc powermodule command signal from the controller. The dc power module cangenerate a rectified DC output signal and provide a dc power modulefeedback signal to the controller. The torch ignition circuitry can bein electrical communication with the dc power module to receive therectified DC output signal and generate the electrical currentsufficient to form the plasma arc.

The controller can provide a command signal corresponding to a desiredrectified DC output signal to the dc power module. The controller canprovide a command signal to the dc power module to ramp up or ramp downthe rectified output signal.

The power supply can also include a transformer in electricalcommunication with the input and the controller and a switching supplyin electrical communication with the control transformer and thecontroller. The power supply can also include a heat exchanger. The heatexchanger can have the same electrical potential as the electrode of theplasma arc torch. The heat exchanger includes a coolant, and thecontroller can monitor the flow rate, the flow level, and/or thetemperature of the coolant. The power supply can also include a voltagefeedback card. The voltage feedback card can be in electricalcommunication with the torch ignition circuitry and the controller. Thevoltage feedback card can monitor the rectified DC output signal fromthe dc power module and provide a voltage feedback signal to thecontroller. The voltage feedback card can signal the controller when apilot arc is established, and/or when cutting arc is established.

In another aspect, the invention features a method of controlling apower supply of a plasma arc system which includes a controller inelectrical communication with the power supply. According to the method,a command signal is provided from the controller to the power supply togenerate an electrical current sufficient to form a plasma arc in aplasma arc torch. The electrical current generated by the power supplyis monitored. The command signal provided from the controller to thepower supply is based on the electrical current monitored.

BRIEF DESCRIPTION OF THE FIGURES

The foregoing and other objects, features and advantages of the presentinvention, as well as the invention itself, will be more fullyunderstood from the following description of preferred embodiments, whenread together with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of an automated plasma arc system.

FIG. 2 is a schematic diagram of a closely-coupled plasma arc systemaccording to one embodiment of the present invention.

FIG. 3 is a flow chart illustrating a screen hierarchy of the controlleraccording to one embodiment of the present invention.

FIG. 4 is a screen shot of a controller display screen according to oneembodiment of the present invention.

FIG. 5A is a screen shot of a parametric shape library for use in acontroller according to one embodiment of the present invention.

FIG. 5B is a screen shot of a change consumables screen of a controlleraccording to one embodiment of the present invention.

FIG. 6 is a block diagram illustrating a closed-loop power supplyaccording to one embodiment of the present invention.

FIG. 7A is a schematic diagram of a side view of a closed-loop powersupply according to one embodiment of the present invention.

FIG. 7B is a schematic diagram of another side view of a closed-looppower supply according to one embodiment of the present invention.

FIG. 7C is a schematic diagram of a top view of a closed-loop powersupply according to one embodiment of the present invention.

FIG. 8 is a schematic diagram of a top view of an automatic processcontroller according to one embodiment of the present invention.

FIG. 9 is a block diagram illustrating an automatic process controlleraccording to one embodiment of the present invention.

FIG. 10A is a cross-sectional view of a proportional flow control valveaccording to one embodiment of the present invention.

FIG. 10B is an exploded view of region A from FIG. 10A according to oneembodiment of the present invention.

FIG. 11A is a schematic diagram of a side view of an automatic processcontroller according to one embodiment of the present invention.

FIG. 11B is a schematic diagram of another side view of an automaticprocess controller according to one embodiment of the present invention.

FIG. 12A is a schematic diagram of another side view of an automaticprocess controller according to one embodiment of the present invention.

FIG. 12B is a schematic diagram of yet another side view of an automaticprocess controller according to one embodiment of the present invention.

FIG. 13 is a schematic diagram illustrating an interaction between atorch height controller, a power supply and a CNC according to oneembodiment of the present invention.

FIG. 14 is a block diagram illustrating a torch height controlleraccording to one embodiment of the present invention.

FIG. 15 is a flow chart illustrating a closely-coupled plasma processaccording to one embodiment of the present invention.

FIG. 16 is a flow chart illustrating a part program execution accordingto one embodiment of the present invention.

FIG. 17 is a flow chart illustrating control of a drive system accordingto one embodiment of the present invention.

FIG. 18 is a flow chart illustrating control of a torch height controlaccording to one embodiment of the present invention.

FIG. 19 is a flow chart illustrating control of a power supply accordingto one embodiment of the present invention.

FIG. 20 is a flow chart illustrating control of automatic processcontrol according to one embodiment of the present invention.

DETAILED DESCRIPTION

The present invention relates to a centralized control architecture fora plasma cutting system, in which the “intelligence” of the system isintegrated into a single controller. The centralized controlarchitecture eliminates redundant hardware and software and integratesthe entire system, thereby improving performance and reducing cycletime. The plasma arc system including the centralized controlarchitecture, will be referred to herein as a closely-coupled plasma arcsystem or simply a plasma arc system.

Referring to FIG. 2, a closely-coupled plasma arc system 10 includes acomputerized numeric controller (CNC) 12 display screen 13, a powersupply 14, an automatic process controller 16, a torch height controller18, a drive system 20, a cutting table 22, and a plasma arc torch 24.

In general, the CNC 12 controls the motion of the plasma arc torch 24over the cutting table 22 and the timing of the cutting process as theprocess relates to the motion. In the present invention, the CNC 12 iscapable of controlling, not only the motion of the plasma arc torch 24,but also the operation of the other components of the plasma arc system10, as well as other cutting processes. The various components of theplasma arc system 10 can be controlled by the CNC 12 concurrently.

The CNC 12 interfaces with the user. The CNC 12 allows the user toselect or provide certain process parameters. The CNC 12 generates otherprocess parameters necessary to operate the plasma arc system 10 basedon the user selection and/or input. A cut program 600 as later shown inFIG. 16, provides part specific information for torch motion and cuttingarc operation. The CNC 12 commands the power supply 14, the automaticprocess controller 16, the torch height controller 18 and the drivesystem 20 to operate. The CNC 12 also monitors certain processconditions to determine whether the plasma arc system 10 is operatingproperly. Based on the monitored information, the CNC 12 adjusts theoperation of the other components of the plasma arc system 10, ifnecessary. Details of the CNC 12 will be described in greater detail inreference to FIGS. 3, 4, 5A-5B, and 15-20.

The power supply 14 generates a high frequency signal sufficient toionize a gas to generate a plasma arc and a DC signal to maintain thearc. In the present invention, all intelligence and adjustment controlsfor configuring the cut process typically provided in a power supplyhave been migrated into the CNC 12 and/or the automatic processcontroller 16. Upon receiving an appropriate command signal from theCNC, the power supply 14 transforms an input signal into an outputsignal sufficient to generate and maintain a plasma arc. Severalcomponents of the power supply 14, including the output generated by thepower supply 14 are controlled by the CNC 12 through a feedbackmechanism. The power supply 14 will be discussed in greater detail inreference to FIGS. 6 and 7A-7C.

The automatic process controller 16 is designed to replace the manualgas flow controls that are normally located at the power supply and/or agas control module. The automatic process controller 16 includesproportional flow control valves to control the flow rate of the cut gasand the shield gas. The-automatic process controller 16 also includespressure transducers for measuring the pressure of the cut gas and theshield gas. This pressure information is provided to the CNC 12, whichin turn adjusts the proportional flow control valves if necessary tochange the flow rates. The intelligence of the automatic processcontroller 16 is also located at the CNC 12. The automatic processcontroller 16 is described in greater detail in reference to FIGS. 8-12.

The torch height controller 18 controls the standoff between the torch24 and the work piece. Unlike a conventional torch height controller 18,however, the intelligence of the torch height controller 18 is migratedinto the CNC 12. The torch height controller 18 is controlled directlyfrom the CNC 12 as a separate servo axis in a manner similar to thedrive system 20 in a conventional plasma arc system. The CNC 12 providesa command signal to the torch height controller 18 to adjust thestandoff, based on the arc voltage measured at the plasma arc torch 24.The torch height controller 18 is described in greater detail inreference to FIGS. 13 and 14.

The drive system 20 receives command signals from the CNC to move theplasma arc torch 24 in an x or y direction over the cutting table 22.The cutting table 22 supports a work piece. The plasma arc torch 24 ismounted to the torch height controller 18 which is mounted to the gantry26. The drive system 20 moves the gantry 26 relative to the table 22 andmoves the plasma arc torch 24 along the gantry 26. The information aboutthe position of the plasma arc torch 24 is provided to the CNC 12. Thus,the CNC 12 allows interactive response and maintains an accurate cutpath. Operation of the drive system 20 and the cutting table 22 do notconstitute an inventive aspect of the present invention and are wellknown to those skilled in the art.

The Computer Numeric Controller

The CNC 12 includes a display, a hard disk, a microprocessor, and randomaccess memory (RAM). The display, for example, can be a Video GraphicArray (VGA) color Double Super Twisted Nematic (DSTN) liquid crystaldisplay (LCD) or an active matrix thin-film-transistor (TFT) display.The CNC 12, for example, can include 2.1 Gigabytes of hard disk andoptionally also include a floppy disk drive. The microprocessor, forexample, can be 166 MHz Pentium® processor. The CNC 12, for example, caninclude 32 Mbytes of random access memory (RAM). The CNC 12 can alsoinclude conductor lines for interface signals for cutting (e.g., gascontrol) and motion logic (e.g., tracing system, markers, homing). Themotion logic can include logic for tracing systems which direct thetorch 24 by tracing a drawing or part. The motion logic can includelogic for marking a work piece. The motion logic can also include logicfor moving the torch to a home position to provide exact locationinformation to the CNC 12.

The programming and operation of the CNC 12 is menu driven. An examplescreen hierarchy is illustrated in FIG. 3. In the example shown in FIG.3, the screen hierarchy is divided into main screen, setups, and shapemanager. The main screen, in part, allows a user to select options suchas files of information to load or save, choices of part options and toelect manual operation of the closely-coupled plasma arc system 10. Thesetups screen, in part, allows selection of cutting parameters such asthe cut gas to be used. The shape manager, in part, allows the user toselect cut patterns from a shape library. The CNC 12 includes agraphical user interface for the user to input certain processparameters. For example, the user can provide information about the typeof power supply, the type of torch, the type of material to be cut, thesetting for the current, the type of plasma gas and the shield gas, thecutting surface (e.g., above water), the thickness of the material to becut, and whether the water muffler is installed as shown in FIG. 4. Theuser can also select any of a number of shapes for cutting from aparametric shape library, along with the desired dimension. An exampleof a parametric shape library is provided in FIG. 5A.

Based on the user input process parameters, the CNC 12 generates otherprocess parameters. These process parameters can be provided from afactory pre-set database or a user defined database. The generatedprocess parameters can include cut speed, kerf diameter, set arcvoltage, cut height, pierce height, and the number of retries upontransfer failure. The process parameters can also include pressuresettings for the cut gas and the shield gas during pre-flow, ignition,cut-flow, ramp-down, shut-off, and post-flow. The process parameters canfurther include settings for the duration of the post-flow, supply-on,pre-flow, purge, pierce, creep, and ramp-down delay. FIG. 4 shows otherprocess parameters generated in response to the user input processparameters. Upon receiving the user input to initiate the plasma arcsystem 10 and generating all of the parameters necessary to start theoperation of the plasma arc system, the CNC 12 executes softwareprograms to initiate and control the operation of the various componentsof the plasma arc system 10. The software program will be discussed ingreater detail in reference to FIGS. 15-20.

In one embodiment, the CNC 12 includes a database for tracking andrecording consumable life. For example, if a new electrode or nozzle isplaced in the plasma torch, this information is provided to the CNC 12.The database will record the date and time the consumable was changedand how long it lasted in minutes, pierces, inches and millimeters. Anexample of a change consumable screen provided by the CNC is shown inFIG. 5B.

Power Supply

The purpose of a power supply 14 is to combine electrical power andgases to create an ionized gas for metal cutting. FIG. 6 shows anembodiment of the power supply 14 of the current invention. Theelectrical power of the power supply 14 is controlled by the CNC 12(shown in FIG. 2), and the gas supply is controlled by the APC 16 (shownin FIG. 2).

Referring to FIG. 6, the power supply 14 includes a three phase powersupply input 30. The three phase power supply input 30 is in electricalcommunication with a main contactor switch 32. The main contactor switch32 is in electrical communication with a main transformer 34. The maintransformer 34 is in electrical communication with a dc power module.The dc power module can be a chopper, an invertor or a siliconcontrolled rectifier. In the embodiment illustrated in FIG. 6, the dcpower modules are a first chopper module 36 and a second chopper module38. The first chopper module 36 and second chopper module 38 are inelectrical communication with a first chopper inductor 35 and a secondchopper inductor 37. The chopper inductors 35, 37 are in electricalcommunication with surge injection and torch ignition circuitry module40. The surge injection and torch ignition circuitry module 40 is inelectrical communication with the cathode manifold 42 which is inelectrical connection with a torch power and coolant lead 43. A voltagefeedback card 52 is in electrical communication with the surge injectionand torch ignition circuitry module 40.

The power supply 14 also includes a control transformer 46 which is inelectrical communication with the three phase power supply input 30. Thecontrol transformer 46 is in electrical communication with a switchingsupply 48 and a heat exchanger/cooler unit 50. A pair of coolant leads58, 60 extend from the heat exchanger cooler unit 50 and the cathodemanifold 42.

The power supply 14 also includes a gas manifold 54. A pilot arc lead 56extends from the surge injection and torch ignition circuitry module 40to the gas manifold 54. A shield gas and pilot arc lead 62 extends fromthe-gas manifold 54 to the torch lead 44. The cut gas leads 64, 66extend from the cut gas sources 68′, 68″ through the power supply 14 tothe torch lead 44.

In operation, the three phase power supply input 30 receives an inputsignal. The input signal can be an AC signal within a voltage range fromabout 200 volts to 600 volts. The input 30 provides power to the maintransformer 34 through the main contactor switch 32. The maintransformer 34 converts the incoming power through two secondarywindings (not shown). Each winding provides power to the chopper modules36, 38. For example, the main transformer can provide 210 VAC signal toeach chopper module 36, 38. The chopper modules 36, 38 provide thecutting voltage supplied to the torch 24. The three phase power supplyinput 30 also provides power to the control transformer 46 whichconverts the incoming power through two secondary windings (not shown)of the control transformer 46. The two secondary windings of the controltransformer 46 provide power to both the heat exchanger or unit 50 andthe switching supply 48. For example, the control transformer 46 canprovide 120 VAC signal to the switch power supply 48 and 240 VAC signalto the heat exchanger/cooler unit 50. The switching supply 48 provides24 VAC signal to the CNC 12 to provide additional power the CNC 12.

The chopper inductors 35, 37 provide rectified DC output signal tosustain the electric arc at the torch 24. The surge injection and torchignition circuitry 40 provides the high frequency and initial surgecurrent to ignite the torch 24.

The DC output signals of the chopper inductors 35, 37 are monitored bythe voltage feedback card 52. When the power supply 14 is energized viathe main contactor switch 52, the voltage feedback card 32 signals theCNC 12 that the power supply 14 is ready. When a pilot arc isestablished, the voltage feedback card 52 signals the CNC 12. When thecutting arc is established, the voltage feedback card 52 signals the CNC12 to begin motion. Once transfer of the arc has occurred and motion isengaged, the voltage feedback card 52 is used to provide voltagefeedback to the CNC 12, and the arc voltage is adjusted by the CNC 12using the torch height control 18. If there is any failure during thisprocess, the failure is detected by the CNC 12, the process is halted,and an error message is posted by the CNC 12.

The power supply 14 can operate in one of several ways. One way ofoperating the power supply 14 is in a full auto-mode. Once a partprogram and plasma process has been selected by the operator, simplypush the START button and the CNC 12 will check to see if the powersupply 14 is on and, if not, will energize the power supply 14 andverify its status. The CNC 12 will then continue executing the partprogram as normal. Any fault condition results in a power supply shutdown, and an error message is provided to the operator.

The second way of operating the power supply 14 is in a remote manualmode. The operator can manually energize the power supply 14 by going tothe diagnostics screen in the CNC 12 and selecting SUPPLY ON. Thisallows remote diagnostics and testing to be performed.

The third way of turning on the power supply 14 is in a local manualmode. A properly trained service agent can manually energize the powersupply by opening the power supply 14 and engaging the SUPPLY ON relay.

During the power up sequence for the power supply 14, the CNC 12receives signals that confirm the presence of the three phase powersupply input 30. Without the signal from the power supply 14, the CNC 12will time out, shut down, and alert the operator. In addition, all ofthe power supply's functions can be manually tested remotely from theCNC 12 by using the diagnostic screens provided by the CNC 12.

The voltage feedback card 52 can monitor the arc voltage at the plasmaarc torch 24 remotely during a cut and use that information as afeedback signal to the torch height controller (THC) 18. Because the CNC12 controls all aspects of the power supply's functions, the voltagefeedback card 52 can also perform other functions provided herein.

Once the start command has been given, the CNC 12 will energize the maincontactor switch 32, allowing the choppers 36, 38 to charge their outputto a full open circuit voltage. The full open circuit is detected by thevoltage feedback card 52 and the information is relayed to the CNC 12.If the full open circuit is within tolerance, and all other parametersare satisfied, the CNC 12 enables the choppers 36, 38 and passes downthe output current set point. The CNC 12 then engages the surgeinjection/torch ignition circuitry 40 to generate a high frequencysignal and enables pilot arc relay. In some embodiments the torch 24 mayhave a spring loaded mechanism to bring the electrode and nozzle incontact to form a pilot arc. When the pilot arc is established at thetorch 24, the output voltage changes, and is detected by the voltagefeedback card 52. The voltage feedback card 52 relays the voltage changeto the CNC 12. As the arc stretches outward to the workpiece, iteventually contacts the workpiece, and the corresponding change involtage is also detected by the voltage feedback card 52 which relaysthis information to the CNC 12. The CNC 12 uses this information as thearc transfer signal and proceeds with the piercing operation.

Once the piercing operation is completed and full machine motion isengaged and stable, the voltage feedback card 52 reverts back to itsoriginal function of torch height controller 18. A fault in any of theabove conditions generates an appropriate error message to the operatorand the system 10 returns to STANDBY mode.

The power supply 14 includes a novel cooling system. In a typicalcooling system, a pump, a tank and other components are tied to chassisground for safety reasons. Since the electrode is at an elevated voltagelevel during the plasma cutting operation, electrolysis occurs withinthe torch leads. Testing has shown that more than 95% of coolant loss isdue to electrolysis. The heat exchanger/cooler unit 50 in the powersupply 14 has been designed to eliminate electrolysis. By tying all ofthe heat exchanger/cooler unit 50 components to the electrode'spotential, electrolysis can be prevented and the coolant can bepreserved. Safety is maintained by placing the heat exchanger/coolerunit 50 within a separate enclosure with appropriate labeling.

The CNC 12 can directly monitor the flow rate, flow level, andtemperature of the coolant and can intelligently respond to each faultsituation to correct any deficiency. In the event of an over-temperaturesituation, the CNC 12 will allow the cutting operation to complete itscurrent task. Afterward, the CNC 12 will alert the operator and commandthe power supply 14 to a STANDBY condition. This allows the power supply14 to remain on and keep the fans running to cool down the coolant, butdisables the output of the power supply 14. If the coolant level dropstoo low, the CNC 12 will allow the cutting operation to complete itscurrent task. Afterward, the CNC 12 will alert the operator and commandthe power supply 14 to turn off. The CNC 12 will not allow the powersupply 14 to turn on again until the low coolant level condition hasbeen satisfied. If the CNC 12 detects loss of coolant flow, it willimmediately end the cutting operation, shut down the power supply 14,and alert the operator.

The CNC 12 has a direct link to the choppers 36, 38 within the powersupply 14 and feeds the choppers 36, 38 an analog signal proportional tothe output current desired. This allows a near-infinite resolution inthe current output. During such operations as ramp-up or ramp-down ofthe output current, very smooth transitions are possible. This reducesthe stress on the consumables within the torch, thereby extending theuseful life of the consumables.

FIGS. 7A-7C show physical placement of each of the components of thepower supply 14. The specific placements of the components provided inFIGS. 7A-7C are exemplary only and other placements can be used inaccordance with the present invention.

Automatic Process Controller

The automatic process controller 16 receives command signals from thecomputerized numeric controller (CNC) 12 to control the flow of gasesinto the plasma arc torch 24. The automatic process controller 16eliminates the need for manually operated gas flow controls, typicallylocated at the plasma power supply. The automatic process controller 16replaces solenoid valves typically located at the power supply and/orgas control module with proportional flow control (PFC) valves that arelocated immediately prior to the body of the plasma arc torch 24.

FIG. 8 shows a top view of the automatic process controller 16. Forclarity, gas hoses and hose connections are not shown. The automaticprocess controller 16 includes gas manifolds 70, 71, valves 72, 73, 74,75, pressure transducers 76, 77, a pressure switch 78, and a bracket 79for mounting the automatic process controller 16 to the torch heightcontroller 18 shown in FIG. 13.

Referring to FIGS. 8 and 9, the automatic process controller 16 includesa first manifold 70 and a second manifold 71. The first manifold 70 is achamber that allows blending and adjustment of one or more cut gassesprovided to the plasma arc torch 24 through the use of flow control. Thesecond manifold 71 is a chamber that allows adjustment of a shield gasprovided to the plasma arc torch through the use of flow control. Theautomatic process controller 16 also includes a first proportional flowcontrol (PFC) valve 72, a second proportional flow control (PFC) valve73, and a third proportional flow control (PFC) valve 74. The first PFCvalve 72 and the second PFC valve 73 are in physical communication withthe first manifold 70. The first PFC valve 72 controls flow of a firstcut gas. The second PFC valve 73 controls flow of a second cut gas. Forexample, the first cut gas can be nitrogen, and the second cut gas canbe oxygen. The first cut gas and the second cut gas can be mixed in thefirst manifold 70.

The third PCF valve 74 is in physical communication with the secondmanifold 71, which is also in physical communication with a controlledsolenoid valve 75. The controlled solenoid valve 75 controls applicationof a shield gas to the plasma arc torch. For example, the shield gas canbe air. A portion of the shield gas can be vented to the atmosphere. Thethird PFC valve 74 controls the amount of shield gas vented to theatmosphere. Thus, the shield gas flow is controlled by purging theexcess gas to the atmosphere.

The automatic process controller 16 can further include a first pressuretransducer 76 and a second pressure transducer 77. Referring to FIG. 9,the first pressure transducer 76 taps into the line 81 inside the firstmanifold. The first pressure transducer 76 monitors an outlet pressureof either the first cut gas, the second cut gas, or a mixture of thefirst cut gas and the second cut gas. The pressure measurement from thefirst transducer 76 is provided to the CNC 12 as feedback. The CNC 12can provide an adjustment command to the first PFC valve 72 and/or thesecond PFC valve 73 to adjust the cut gas flows if necessary. The secondpressure transducer 77 is tapped into the line 82 inside the secondmanifold 71. The second pressure transducer 77 monitors the outletpressure of the shield gas provided to the plasma arc torch 24. Thepressure measurement from the second transducer 77 is provided to theCNC 12 as feedback. The CNC 12 can provide an adjustment command to thethird PFC valve 74 to control the flow of the shield gas if necessary.

In operation, a user selects a cut program among many programs stored inthe CNC 12 and selects certain process variables. For example, the usercan select eight process variables. As discussed in reference to FIG. 4,these eight process variables include a power supply type, a torch type,a material type, a current setting, a plasma/shield gas type, a cuttingsurface, a material thickness and an installation of water muffler. TheCNC 12 accesses an internal database and sets and adjusts the flow ratesof the cut gas and the shield gas based on the process variablesprovided by the user. The database can be a factory default database ora user defined database. An example CNC display which illustratesparameter for gas control is shown in FIG. 4.

The CNC 12 provides command signals to the first PFC valve 72, thesecond PFC valve 73, the third PFC valve 74, and the controlled solenoidvalve 75. In response to the command signals, the first PFC valve 72,the second PFC valve 73, and the third PFC valve 74 can adjust the flowof the applicable gas. A proportional solenoid valve allows the flowthrough the proportional solenoid valve to be controlled variably asopposed to a standard solenoid valve that is either completely closed orcompletely open. The structure and operation of an exemplaryproportional solenoid valves are described in detail in U.S. Pat. No.5,232,196, the contents of which are herein incorporated by reference.

Referring to FIGS. 10A and 10B, a proportional solenoid valve includes asolenoid coil 138, an armature assembly 124, a yolk 140, a pole 134 anda flat spring 132. As the solenoid coil 138 is energized, the coilmagnetomotive force induces a flux through yoke 140 and pole 134, acrossa working gap 135, through armature assembly 124, and back to yoke 140via flux concentrator 148. The magnetic flux induces a force ofattraction between the armature assembly 124 and the pole piece 134,causing the armature assembly 124 to move towards pole piece 134. As thearmature assembly 124 displaces towards pole piece 134 and away fromorifice 122 in the valve body 112, the flat spring 132 opposes thesolenoid force and controls the magnitude of the net deflection of thearmature assembly 124. Increasing the coil current increases the forceof attraction between the armature assembly 124 and the pole piece 134,thereby increasing the movement of the armature assembly 124 towardspole piece 134. The flat spring 132 provides resistance to the forceinduced by the solenoid coil 138. The flat spring 132 is three-lobed andis constrained on its outer diameter in one of the six degrees offreedom. FIG. 10B illustrates how the outside diameter of the flatspring 132 is held between an O-ring 130 and a ledge of the armatureassembly 178. As current is increased to the coil, the flow output ofthe valve increases proportionally. As current is decreased, the flow isdecreased proportionally. The PFC valve described in reference to FIGS.10A and 10B is exemplary only. Proportional solenoid valves operatingunder other principles or incorporating other structures can also beused in accordance with the present invention.

The solenoid valve 75 opens or closes depending on the command signalfrom the CNC 12. The solenoid valve 75 is a simpler valve than theproportional solenoid valves 72, 73, 74. The solenoid valve 75 does nothave the flat spring configuration described in the proportionalsolenoid valves 72, 73, 74 to enable proportional flow control. Instead,the solenoid valve 75 has two positions, an open position and a closedposition. For example, when the command signal is at state zero, thesolenoid valve 75 is closed. When the command signal is at state one,the solenoid valve 75 is open.

The output of the gasses passing through the PFC valves 72, 73, 74 andthe solenoid valve 75 are monitored by the pressure transducers 76, 77and this information is communicated to the CNC 12. If necessary, theCNC 12 adjusts the command signals provided to the PFC valves 72, 73, 74and the solenoid valve 75, thereby creating a closed-loop dynamicrelationship between the CNC 12 and the automatic process controller 16.This dynamic relationship improves the plasma cutting process by moreaccurately controlling the plasma gas and shield gas flow into theplasma arc torch 24.

The pressure information gathered by the pressure transducers 76, 77 canalso be used in adjusting other process parameters. In one embodiment,the motion speed and profile within a cut program 600 (FIG. 16) is usedto adjust the process parameters for the automatic process controller 16and torch height controller 18. For example, during a corner cuttingoperation, where the torch 24 enters and exits a corner, the speed ofthe torch 24 must be decreased and then increased, respectively. Duringthis corner cutting operation, the zone of reduced speed causes the arcto remove too much material from the work piece resulting in a widerkerf width, inaccurate finished part dimensions, and a reductions inconsumable life. The CNC 12 can now use the knowledge contained withinthe cut program 600 regarding cut path and speed, and adjust gas flowsusing the automatic process controller 16. The adjustment in gas flowthen dictates a change in the arc current level from the power supply 14and a change in the torch height using the torch height controller 18.These adjustments further dictate a change in cut program's 600 cut pathto compensate for the change in kerf width. The result is an integratedcutting process.

In one embodiment, the automatic process controller 12 includes a safetyfeedback feature. In one embodiment, the safety feedback featuremonitors air pressure at the shield cap by routing the shield gasthrough an orifice 83 provided in the line 80 passing through the secondmanifold 71. The orifice 83 restricts the shield gas flow. If the cap isremoved the pressure drop is then monitored by a pressure safety switch78. The pressure safety switch 78 indicates that the shield cap has beenremoved by sensing the pressure at the cap. If the proper pressure isnot maintained at the shield cap, the power supply 14 is disabled and anerror message appears on the CNC display 13. This safety feedbackfeature ensures that the shield cap is in place prior to starting thepower supply 14 or when the power supply 14 is in use. The firstpressure transducer 76 and the second pressure transducer 77 also act assafety monitors to ensure proper gas flow. If proper gas flow is notmaintained, the process can be shut down by the CNC 12.

In one embodiment, the automatic process controller 16 also includes ashield gas diverter manifold 84 shown in FIGS. 1A and 1B. The purpose ofthe shield gas diverter manifold 84 is to separate the shield gas fromthe pilot arc wire which are coupled in a line 62 extending from thepower supply 14 shown in FIG. 6. The shield gas diverter manifold 84 isattached to the bracket 79. The bracket 79 is also attached to theshield gas manifold 71 and the cut gas manifold 70 of the automaticprocess controller 16. The shield gas diverter manifold 84 keeps thepilot arc wire away from the automatic process controller 16. Shield gastravels from the shield gas diverter manifold 84 to the automaticprocess controller 16 through line 85. The flow of shield gas is thenadjusted in the shield gas manifold 71, and the adjusted shield gas isreturned from the shield gas manifold 71 of the automatic processcontroller 16 to the shield gas diverter manifold 84 through line 86.The adjusted shield gas is then fed into one end of the torch lead 87which also contains the pilot arc lead. The other end of the torch lead87 is connected to the torch 24 for supplying the adjusted shield gas tothe torch 24 as well as for placing the pilot arc lead into electricalcontact with the torch nozzle. FIGS. 12A and 12B show a nitrogen line 64and an oxygen line 66 supplying cut gas to the cut gas manifold 70. Fromthe cut gas manifold 70, the cut gas is supplied to the torch 24 by line90.

The automatic process controller 16 described herein provides severaladvantages. First, the cut quality is improved. The closed-loopexecution of the cutting process based on monitoring the gas flow andcontrolling the gas flow based on continuous feedback improves cutquality. Automatic control, in contrast to manual control, of gas flowvalves also improves accuracy. In addition, short leads from themanifolds 70, 71 to the plasma arc torch 24 provides nearlyinstantaneous response, further improving cut quality. Second, cycletime of the operation of the plasma arc system is reduced, sinceoperator intervention is minimal and time for purging the gases is shortdue to reduced distance between the manifolds 70, 71 and the plasma arctorch 24. For example, typical plasma arc systems require purge time ofseveral seconds in duration. The present invention, on the other hand,can establish a stable gas condition in less than about 200milliseconds. By establishing a stable gas condition in a shorter periodof time, the automatic process controller improves consumable life byminimizing unstable gas conditions. Third, the automatic processcontroller includes safety features. For example, the present inventionprevents ignition of the plasma arc if there is insufficient gas flow,and generates an error message on the CNC display to alert the user. Thepresent invention also disallows out-of-tolerance flow conditions,allowing the CNC to safely shut down the system without damaging theconsumables of the plasma torch.

Torch Height Control

The purpose of a torch height controller 18 is to provide an optimumvoltage for a desired metal cutting process. There is a directrelationship between cut voltage and a standoff. The standoff refers tothe gap between the metal work surface and the torch electrode.

Referring to FIGS. 13 and 14, the torch height controller (THC) 18includes a mechanical slider or lifter 90 driven by a motor 91. Themotor 91 is in electrical communication with the CNC 12. The plasma arctorch 24 is attached to the slider 90. An encoder provided inside themotor 91 is in electrical communication with the CNC 12. The encoderprovides location information from the slider 90 back to the CNC 12. Thetorch 24 is in electrical communication with the voltage feedback card52 provided inside the power source 14 and the CNC 12 to provide voltageinformation to the CNC 12. The CNC 12 uses the location informationprovided by the encoder, and voltage information provided by the voltagefeedback card 52, in conjunction with a desired work piece cut pathprogrammed into the CNC 12, to provide an input signal to the motor 91to change the standoff.

To start the cutting process, the CNC 12 lowers the torch 24 untilcontact is made with a work piece 92. Once the torch 24 contacts thework piece 92, a signal is sent from the voltage feedback card 52 to theCNC 12 to indicate the position of the work piece 92.

After the torch 24 has contacted the work piece 92, the torch 24 isretracted to a pierce height as determined by the CNC 12. After thepilot arc in the torch 24 has transferred to a cutting arc, a signal 94is sent from the voltage feedback card 52 to the CNC 12 allowing the CNC12 to control the motion of the torch height controller 18.

The voltage feedback card 52 reduces the voltage read at the torch 24 bya ratio, which for example can be 40:1, to provide a low voltage signal94 to the CNC 12. The CNC 12 then multiplies the reduced voltage by theinverse of the ratio of voltage reduction used in the voltage feedbackcard 52 to determine the exact cutting arc voltage. If the cutting arcvoltage is not at a set voltage as determined by the CNC 12, based on agiven part cutting program, the CNC 12 will send a signal 95 to themotor 91 to adjust the torch height controller 18 up or down to adjustthe voltage. If the THC 18 is unable to respond to a command 95 from theCNC 12, or the cutting voltage is outside of set voltage tolerancesprogrammed into the CNC 12, the CNC 12 will stop the present operationand post a fault message to the operator on a CNC display screen 13.

At the end of a cut segment, the torch 24 will be raised to travel overobstacles before beginning the initial pierce cycle for the next workpiece, as the torch 24 can be programmed to be raised between workpieces. If the travel distance to the next part is short, as determinedby the user, the full retraction and initial plate sensing may bebypassed allowing immediate positioning of the THC 18 at a pierce heightand voltage to begin the next cutting cycle. This feature significantlyimproves the overall process time for cutting separate work pieces 92 ona plate.

In operation, if the torch 24 passes over an area on the plate wherethere is no metal, for example off the edge of a work piece 92, the CNC12 will detect a large voltage spike. In response to the voltage spike,the CNC 12 will prevent motion of the THC 18 to prevent the THC 18 fromdriving the torch 24 into the workpiece 92.

In areas where the motion profile for a workpiece 92 is very intricate,for example sharp angles or curves, the torch motion will slow-down.This slow down in torch motion causes more metal to be removed along thecut path which results in a wider cut path and increased voltage. TheCNC 12 will prevent motion of THC 18 in areas with intricate motionprofiles to prevent the THC 18 from driving the torch 24 into theworkpiece 92.

In the event of a loss of the cutting arc, the loss is detected by theCNC 12 from a signal sent by the voltage feedback card 52, and the CNC12 halts the cutting process and sends an error message to the operatoron the display screen 13 of the CNC 12.

The CNC Programs

Upon receiving the user input to initiate the plasma arc system andgenerating all the parameters necessary to start the operation of theplasma arc system, the CNC 12 provides command signals to and receivesfeedback signals from each of the drive system 20, the torch heightcontroller 18, the power supply 14 and the automatic process controller16 as illustrated in FIG. 15. The CNC executes the routines illustratedin FIGS. 16-20. For example, the CNC performs these routines at 1millisecond intervals for as long as the system is in operation.

The CNC executes the part program to provide information to theclosely-coupled plasma arc system 10 for cutting a desired shape in aworkpiece. Referring to the flow chart shown in FIG. 16, upon receivingthe start command (step 605), the CNC 12 checks a cut program todetermine if the cut program has been completed (step 610). If all theoperations are completed, the program ends (step 615). If the cutprogram is not completed, the CNC 12 then checks the motion segment ofthe cut program to determine if the gantry and torch must be moved. Ifthe gantry and torch must be moved, the CNC 12 provides a command tomove the gantry and torch (step 620), and then the CNC 12 returns tocheck program (step 610) to determine if the cut program has beencompleted. If the gantry and torch do not have to be moved, the CNC 12then determines if the plasma arc must be cut off. If the plasma arcmust be cut off, the CNC 12 provides a command to stop the plasma arc(step 625) and then the CNC 12 returns to check program (step 610) todetermine if the cut program has been completed. If the plasma arc doesnot have to be cut off, the program then checks to see if the plasma archas to be started. If the plasma arc does not have to be started, theCNC 12 returns to check program (step 610) to determine if the cutprogram has been completed. If the plasma arc has to be started, the CNC12 provides a command to start the plasma arc (step 630), and checks forarc transfer from the pilot arc to the work piece 633. If the arc hastransferred to the work piece, the CNC 12 returns to the check program(step 610) to determine if the cut program has been completed. If thepilot arc does not transfer, the CNC 12 checks the number of retries(step 635). If the number of retry counts has been exceeded, an errormessage is displayed on the CNC display (step 640). If the number ofretries has not been exceeded, the number of retries is incremented(step 645) and the plasma arc start (step 635) is retried.

The CNC 12 executes a routine illustrated in FIG. 17 for operating thedrive system. Referring to the flow chart shown in FIG. 17, uponreceiving the start command (step 700), the CNC 12 checks the overtravelswitches located at each end of the gantry and the rail (step 701). Ifthe overtravel switches are active, then a feedback signal is providedto the CNC 12 to disable the system 10 (step 702) and to generate anerror message on the display 13 of the CNC 12 (step 704). If theovertravel switches are not active, the CNC checks the position of thetorch 24 and the gantry 26 using an encoder in a servo loop with themotors (step 706). If the position is accurate, a single run through theroutine for the driver system 20 is complete. If the position isincorrect, the CNC 12 provides a command signal to the driver system 20to move the gantry 26 and/or the torch 24 (step 708). The CNC 12 checksthe speed of the torch system (step 710). If the speed is above plasmahi/lo, above a user defined speed, for example 90% of a design speed(step 712), then the torch height controller 18 is enabled (step 714)and the routine is complete. If the speed is below the user definedspeed, the torch height controller 18 is disabled (step 716) and theroutine is complete. The CNC 12 repeats the routine for the drive system20 for as long as the plasma system is in operation.

The CNC 12 executes a routine illustrated in FIG. 18 for operating thetorch height controller 18. Upon receiving a start signal, the CNC 12checks the operation mode (step 800). If the operation mode is inautomatic mode, the CNC 12 checks to see whether the torch heightcontroller 18 is disabled (step 802). If the torch height controller 18is disabled, the routine is complete. If the torch height controller isnot disabled, the CNC 12 checks the arc voltage (step 804). If the arcvoltage is too high, the torch height controller 18 lowers the plasmaarc torch 24 (step 806) and the routine is complete. If the arc voltageis not too high, the CNC 12 checks the arc voltage to determine whetherthe arc voltage is too low (step 808). If the arc voltage is not toolow, then the routine is complete. If the arc voltage is too low, thenthe torch height controller 18 raises the plasma arc torch 24 (step 810)and the routine is complete. If the torch height controller 18 is not inthe automatic mode (step 800), then the CNC 12 sets the torch height byraising the torch as high as possible to a known location, and then thetorch is lowered to touch the work piece. Then the torch is raised to adesired location and the torch height is checked (step 812). If thetorch height is too high, then the torch height controller lowers theplasma arc torch 24 (step 806) and the routine is complete. If the torchheight is not too high, then the CNC 12 checks to see whether the torchheight is too low. If the torch height is not too low, then the routineis complete. If the torch height is too low, then the torch 24 is raised(step 810) and the routine is complete. The CNC 12 repeats the routinefor the torch height controller 18 for as long as the plasma arc system10 is in operation.

The CNC 12 operates the power supply 14 by executing the routine shownin FIG. 19. The CNC 12 checks the status of the power supply 14 (step900). If the power supply 14 does not have a ready condition, the CNC 12generates an error message (step 902). If the power supply 14 does havea ready condition, the CNC 12 moves on to check coolant flow error (step904). If the coolant flow is too low, then the CNC 12 generates an errormessage (step 906). If the coolant flow is sufficient, the CNC 12 checksthe coolant temperature (step 908). If the coolant temperature is toohigh, the CNC 12 generates an error message (step 910). If the coolanttemperature is sufficient, the CNC 12 checks the coolant level (step912). If the coolant level is too low, the CNC 12 generates an errormessage (step 914). If the coolant level is sufficient, the CNC 12checks the current setting (step 916). If the current setting isincorrect, the CNC 12 sends a command signal to adjust digital to analogconverter located in the controller to send an analog signal to thechopper (step 918). If the current setting is correct, the routine iscomplete. The CNC 12 repeats the routine for controlling the powersource.

The CNC 12 controls the operation of the automatic process controller 16by executing the routine shown in FIG. 20. The CNC 12 checks thepressure of the pressure transducer for the shield gas (step 1000). Ifthe shield gas pressure measured at the transducer is incorrect, the CNC12 generates and applies a command signal to adjust the PFC valve 74(shown in FIG. 8) for the shield gas (step 1002). The CNC 12 checks theshield gas timer located in the CNC 12 (step 1004) and if the shield gastimer has been exceeded, the CNC 12 generates an error message (step1006). If the shield gas timer has not been exceeded, the CNC 12increments the shield gas timer because a fault condition has not beenencountered (step 1008). The CNC 12 moves on to check the cut gaspressure (step 1010). If the shield gas pressure is correct, the CNC 12resets the shield gas timer (step 1012). After resetting the shield gastimer, the CNC 12 checks the cut gas pressure (step 1010) to determineif cut gas pressure is correct. If the cut gas pressure is correct, theCNC 12 resets the cut gas timer (step 1014) and the routine is complete.If the cut gas pressure is incorrect the CNC 12 adjusts PFC valves 72,73 in the cut gas manifold 70 (step 1016). After adjusting the PFCvalves 72, 73 in the cut gas manifold 70, the CNC 12 checks the cut gastimer (step 1018). If the cut gas time has been exceed, the CNC 12generates an error message (step 1020). If the cut gas timer has notbeen exceeded, the CNC 12 increments the cut gas timer (step 1022) andthe routine for controlling the APC 16 is complete. The CNC 12 repeatsthe routine for controlling the APC 16 during the entire operation ofthe torch to control the cut gas flow and the shield gas flow.

Doctrine of Equivalents

While the invention has been particularly shown and described withreference to specific preferred embodiments, it should be understood bythose skilled in the art that various changes in form and detail may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims. For example, thecentralized control architecture described herein can be useful inoperating other metal processing systems, such as a plasma arc weldingsystem.

What is claimed is:
 1. An automatic process controller for a plasma arcsystem, the automatic process controller comprising: a first manifold; afirst proportional flow control valve positioned upstream of the firstmanifold to control a cut gas flow to the first manifold; a secondmanifold; a second proportional flow control valve positioned upstreamof the second manifold to control a shield gas flow to the secondmanifold; a first pressure transducer positioned downstream from thefirst manifold to measure a pressure of the cut gas exiting the firstmanifold; and a second pressure transducer positioned downstream fromthe second manifold to measure a pressure of the shield gas exiting thesecond manifold, wherein the first proportional flow control valve isadjustable based on the pressure of the cut gas measured by the firstpressure transducer for controlling the flow of the cut gas, and thesecond proportional flow control valve is adjustable based on thepressure of the shield gas measured by the second pressure transducerfor controlling the flow of the shield gas.
 2. The automatic processcontroller of claim 1 further comprising a third proportional flowcontrol valve positioned upstream of the first manifold to control asecond cut gas flow to the first manifold.
 3. The automatic processcontroller of claim 1 further comprising a solenoid valve positionedupstream to control the shield gas flow into the second manifold andwherein the second proportional flow control valve controls venting ofan excess shield gas to the atmosphere.
 4. The automatic processcontroller of claim 1 wherein the second manifold further comprises aline for directing the shield gas to a shield cap, the line defining acritical orifice for increasing a pressure of the shield gas directed tothe shield cap.
 5. The automatic process controller of claim 1 furthercomprising a third manifold in fluid communication with the secondmanifold, the third manifold configured to receive a torch leadcomprising a pilot arc wire and a shield gas line, to segregate theshield gas line from the pilot arc wire, and to divert the shield gas tothe second manifold.
 6. The automatic process controller of claim 4further comprising a first pressure switch positioned downstream fromthe second manifold to monitor the pressure of the shield gas passingthrough the critical orifice.